Heat exchanger



y 1962 H. GRENELL ET AL 3,034,204

HEAT EXCHANGER Original Filed July 21, 1950 4 ets-Sheet 1 Fig.2 4

INVENTORS Leland H. Grenell and Huhtlg M. Campbell BY5A g A TTORNE May15, 1962 if 5%., f, I

INVENTORS Leland H.6renell and Huntlg M. Campbell ATTORNEY y 5, 1962 L.H. GRENELL ET AL 3,034,204

HEAT EXCHANGER Original Filed July 21, 1950 4 SheetsSheet 3 INVENTORSLeland H. Grenell and Huntlg M.Compbell ATTORNE y 1962 H. GRENELL I ETAL 3,034,204

HEAT EXCHANGER 4 Sheets-Sheet 4 Original Filed July 21, 1950 INVENTORSLeland H. Grenell and Huntlg M. Campbetl ATTORNEY 0 I Darwin/Rh)" 2 12Claims. (Cl. 29157.3)

This invention relates to heat exchangers and in particular to a methodfor manufacturing heat exchange cores and the like of sheet metal. Thisis a division of copending application Serial No. 552,982 filed December2, 1955, now abandoned, which in turn is a division of co-pendingapplication Serial No. 175,226 filed July 21, 1950, now Patent No.2,759,247.

Tubular type radiator cores for use with internal combustion enginessuch as those used in motor vehicles and airplanes and radiant heatersfor home use have heretofore been manufactured by various methods ofassembling the tubes with fins, and soldering the assembly. For example,one method for manufacturing automotive radiators involves formingopenings in the fins, holding the fins in proper spaced relation, andpushing the individual tubes through the openings in the fins. Such amethod requires that the fin and tube stock be relatively thick in orderto have the necessary strength for the assembling operation. Some suchcores contain as many as between one hundred and two hundred tubes andmore, each of which must be inserted individually by hand. The tubes arecoated with solder and the assembly core is heated to solder the tubesand fins together to improve the strength and heat transfer. Sometimesthe solder connection is faulty and the efliciency of such cores is lowdue to the poor metal to metal contact. Methods have been suggested forimproving the metal to metal contact between the tubes and the fins,such as filling the tubes with water and freezing in order to expand thetube within the opening in the fin, or filling the tubes with a liquidand heating to effect such expansion. These methods of construction andassembly are fraught with various disadvantages among which are, forinstance, high cost of manufacture due to the number and kind ofprocessing steps required and wastage of tubes, fins, and partlyassembled cores, even with skilled operators.

It is therefore an object of this invention to provide an improvedmethod for the economical manufacture of heat exchange cores. Anotherobject is to provide a method of manufacturing and assembling heatexchange cores in which a substantial saving in time of assembly iseffected over prior practice. Another object is to provide a method ofmanufacture facilitating assembly of tubes and fins in heat exhangercores. Still another object is to provide a method of manufacturing heatexchange cores adapted to be carried out mechanically instead ofmanually. A still further object of the invention is to provide a simpleeconomical method for manufacturing heat exchange cores, which cores areof improved design having fins both perpendicular and parallel to thetubes therein. A further object is the provision of heat exchangerssuitable for both radiant and convection heat- The foregoing objects andadvantages, as well as others which may become apparent from thedetailed description hereinafter, are accomplished in accordance withthis invention by providing fins on the surface of a metal sheet havinginternal tubular passageways. The finned sheet is made by providing finson a tube sheet formed by sandwiching a pattern of non-bonding orseparation material between two sheets of metal, forming a single tetlayer of metal between the areas covered by the separation material bypressure welding, and applying a fluid pressure on the inner surfacesheld apart by the separation material to form cavities Within the sheetin accordance with the pattern. Any desired processing may be employedintermediate the aforenamed steps provided such processing does notinterfere with the functioning of said steps. The diameter, length andpositioning of the tubes or cavities formed within the sheet by thefluid pressure and the resulting bulges or ribs on the surface dependmainly upon the pattern dimensions and designs in which the separationmaterial is originally applied. No undesirable voids exist betweenadjacent tubular passageways since the metal of the sheets intermediatethe passageways are forged or pressure welded into one layer of metalforming a web between the passageways of substantially uniformcomposition, or if the sheet has only one passageway the web extends oneither side of the passageway. The web being substantially thicker thanthe tube walls provides a sturdy support for the fins thereon andlikewise is a good conductor for transfering heat from the tubes to thefins. In prior methods only the thin tube walls were available forsupporting the fins, thus requiring thicker walled tubes or leading tofrail structures.

In accordance with the present invention, the fins are supported by theweb but, if desired, they may also be supported by the tube walls. Forexample, if the fins are to encompass the tube walls on one or bothsides of the sheet, it is preferred to first assemble the fins and tubesheets, then to expand the tubes by fluid pressure so as to provide goodmetal to metal contact between the tube wall and fin, and finally toweld the assembly. If the fins encompass the tube walls on both sides ofthe sheet, it is preferred to provide the fins with openings suitablycontoured for the edges thereof to contact the web with an enlargementof the openings in the tube area-s, then to place them in the desiredspaced relation, to coat the sheets containing the separation materialwith tin or other solder or suitable Welding material, then to insertthe sheets through the openings in the fins and then to expand thesheets until the resulting tube walls firmly contact the edges of theopenings in the fins. Welding or soldering of the assembly is thenrelatively simple since the edges of the openings in the fins are infirm contact with the sheet surface and the operation can beaccomplished merely by heating the entire assembly to the soldering orwelding temperature. Each sheet may be so designed as to provide aplurality of tubes, so that the handling of individual tubes is notnecessary. The process of forming the expanded sheet is set forth andclaimed in copending application of Leland H. Grenell, Serial No.128,116, filed November 18, 1949, now Patent No. 2,690,002 issuedSeptember 28, 1954. If the fins do not encompass the tube walls but aremerely supported by the web between the tubes in said sheet, then thefins may be provided on the web either before or after the tubes havebeen expanded. For instance, the fins may be attached to the Web bywelding, or the like, or may be formed of the webitself. In the latterinstance a pattern of separation material other than that utilized informing the tubes may be applied and the web expanded by fluid pressureto form bulges thereon which upon being suitably opened may serve asfins between the tubes.

Having described in the foregoing in a general way the nature andsubstance of this invention, there follows a more detailed descriptionof preferred embodiments theresheet formed when the sheets of metal ofFIGURE 1 have been brought together and hot rolled,

FIGURE 3 is a perspective view illustrating the tube sheet of FIGURE 2after the edge has been opened up in the separation material areas,

FIGURE 4 is a perspective fragmentary view illustrating a partialassembly of fins and tube sheets,

FIGURE 5 is a perspective fragmentary view of a heat exchange coreillustrating the assembly after the tube sheets have been expanded,

FIGURE 6 is a perspective fragmentary view of an expanded tube sheetillustrating another embodiment of this invention,

FIGURE 7 is a perspective fragmentary view of a heat exchange coreillustrating the tube sheet of FIGURE 6 provided with fins,

FIGURE 8 is a plan view of a part of an expanded tube sheet illustratinganother embodiment of the invention,

FIGURE 9 is a perspective fragmentary view of a heat exchange coreillustrating the tube sheet of FIGURE 8 provided with fins,

FIGURE 10 is a plan view of a part of an expanded tube sheetillustrating another embodiment of the invention,

FIGURE 11 is a plan view of a heat exchange core illustrating anotherembodiment of the invention, and

FIGURE 12 is a vertical fragmentary view of the heat exchange core ofFIGURE 11.

Referring to FIGURE-1, for the manufacture of heat exchange devices,sheets 1 and 2 of metal, 0.070 inch thick and composed of 92% to 94%copper, 2.05% to 2.60% iron, phosphorus in amount up to 0.025%, lead inamount up to 0.05% and the balance zinc, are first degreased by emersionin an organic solvent bath, such as naphtha or white glycerine, at roomtemperature and then wiped free of solvent. The sheets are then cleanedin an acid bath containing, for example, approximately one part byvolume of 68% nitric acid, one part by volume of 95% sulphuric acid, andone part by volume of water at room temperature. Such treatment isdesigned to remove any oxide film on the metal, the clean surface on thesheet being desirable in order to secure good bonding in the subsequenthot rolling operation. The sheets are then rinsed thoroughly in' coldwater and subsequently in hot water and air dried at room temperature.

A separation or weld-preventing material 3, consisting of a mixture ofgraphite in water glass, is then applied in a thin layer in spacedstrips throughout the length of sheet 1, the number of strips appliedcorresponding to the number of tubes desired in the finish sheet. Suchseparation material may be sprayed through a masking die, paintedthrough a stencil, squeezed through a silk screen, or applied in anysuitable manner. For instance, if the separation material 3 is to beapplied through a silk screen to the selected area, graphite in theratio of about three to four kilograms to three liters of water glasssolution is satisfactory. A thinner more fluid mixture is, of course,used if the separation material is to be applied by painting or sprayingon the selected areas.

The elongation of the metal during subsequent rolling must be allowedfor in the shape and dimension of the pattern of separation materialoriginally applied to the sheet. For instance, the strip and pattern islengthened in the direction of rolling in substantially inverseproportion to the change in thickness of assembly. Pattern lines thatrun perpendicular to the direction of rolling for instance to formheaders are, therefore, increased in width in substantially inverseproportion to the change in thickness of the assembly. Tube patternlines such as 3 that run in the direction of rolling are not changedappreciably in width. Thus, if one wishes a conduit or header runningperpendicular to the direction of rolling one inch in diameter andtheassembly thickness during the rolling operation is reduced toone-half the original thickness, then the pattern lines runningperpendicular to the direction of rolling must be made only aboutone-half inch wide. The thickness of the layer of separation materialdecreases in direct proportion with the decrease in thickness of theassembly during rolling due to the spreading or elongation of thematerial during the rolling operation. The thickness of the layer ofseparation material after rolling should be suificient to preventbonding of the metal except where such bonding is desired.

After the tube pattern of separation material 3 has een applied to sheet1, the sheet 2 is placed on sheet 1 with the separation material 3between them. If sheet 2 is permitted to move freely in frictionalcontact with the separation material on sheet 1 prior to the subsequenthot rolling operation, the pattern is likely to be damaged or distortedso that the desired conduit system will not be obtained. The sheets aretherefore fastened together to avoid obliteration of the pattern, by anysuitable means, such as heli-arc welding the edges, tacking the edgestogether by spot-welding, or by crimping the edges, or the like.

The assembly is then placed in a furnace and heated to about 900 C. Toprevent oxidation of the inner faces of the sheets 1 and 2, the edges ofthe assembly may be completely sealed as by welding or the like, or aninert or reducing atmosphere may be employed in the furnace if desired;The temperature of 900 C. is about 160 C. below the melting point of thealloy and is suificiently high to effect pressure welding of the twosheets of metal in the hot rolling step to be described hereinafter. Theexact temperature to be used for pressure welding is, of course,dependent upon the melting point of the particular metal or alloyutilized and should be relatively close thereto.

Inasmuch as each sheet of metal, 1 and 2, is 0.070 inch thick and thelayer of separation material 3 is only about 0.002 to 0.005 inch thick,the assembly is about 0.14 inch thick. As soon as the assembly hasreached a temperature of about 900 C. it is hot rolled in one pass to athickness of about 0.070 inch and is then cleaned with acid, washed anddried as described in the foregoing treatment of sheets 1 and 2. It isdesirable to hot roll to a reduction of at least 35% in order to insurewelding of the sheets, and a reduction of approximately 50% in one passis preferable as is described in the foregoing. The welded sheet is thencold rolled to a finish gauge of about 0.048 inch thickness, is thenannealed at a temperature of 750 C. one half hour to remove thehardening elfect of the cold rolling, and is then cleaned by acid,washing, and drying treatments as described hereinbefore. The coldrolling step is carried out in order to accurately control the thinnessof the sheet. If sufiicient accuracy in gauge for the particular use canbe obtained by hot rolling, the entire reduction can be carried out byhot rolling, and the cold rolling and annealing treatments referred toin the foregoing may be omitted. The strength of the sheet formed by thehot rolling step is appreciably greater than that of the cast structureobtained with spot-welding techniques. The cast structure formed byspot-welding contains appreciably larger grains than the sheet prior tosuch welding, whereas thesheet formed by the hot rolling step has agrain size substantially uniform throughout the sheet. The welded sheet4, illustrated in FIGURE 2, is then coated with tin by dipping in amolten bath thereof, and the unbonded edge of the sheet in the areasadjacent the separation material 3 is then pried open mechanically asillustrated at 5, FIGURE 3, 'to permit a nozzle for applying fluidpressure to be inserted therein.

Referring to FIGURE 4, fins 6 are then formed from sheet metal about0.003 inch thick of the alloy composition set forth in the foregoing andhaving suitably shaped openings as illustrated at 7 to permit theinsertion of the tube sheets 4, FIGURE 4, the openings 7 being so shapedas to encompass and contact the subsequently formed tube Walls as wellas the web of the sheet.

The fins are then placed in suitable; spaced relation as in a comb orother suitable die for holding the edges thereof and the tube sheets 4are then inserted in the openings 7, as illustrated in FIGURE 4. Thetube sheets 4 may be inserted individually into the openings 7 by hand,or they may likewise be held in suitable spaced relation in a comb orother suitable die, and all inserted simultaneously into the openings 7.The latter method is preferable from the standpoint of mass production.Nozzles for applying fluid pressure are then inserted in the openings 5in the tube sheets and pressure is applied until the metal in theunwelded inner portions of the sheet containing the separation materialis expanded to provide the tubes, with the walls fitting snugly withinthe opening 7 in the fin 6 as illustrated in FIGURE 5. With the expandedtube walls 9 tightly engaging the edges of the openings 7 in the fin 6,the assembly is heated to a temperature suflicient to cause the tin onthe expanded tube sheet surface to weld or solder the fins to the tubesheet. The finished heat exchange core, FIGURE 5, then has tubes 9 withfins 6 perpendicular thereto and also fins parallel thereto asrepresented by the web 8 of the tube sheet. As will be understood in theart the amount of fluid pressure necessary will vary with the gauge,temper and composition of the metal used.

The tube sheet expands when pressure is applied with litle or nothinning of the cavity wall, the expansion being accomplished by aseparation or opening up of the metal with a resultant decrease of sheetwidth, depending on the design and dimension of the cavities. Therefore,in order for the tube walls to engage the fin properly it is desirableto take into account such creeping of the sheet 4 during expansion bydesigning pear-shaped or ovoid openings 7 in the fin 6. Such creepingphenomena can be avoided if desired, of course, by suitably holding theedges of the sheet 4 stationary and effecting the expansion by athinning of the tube wall. The shrinkage in width of sheet 4 duringexpansion is illustrated in FIGURE 5, as leaving an opening 40 betweenthe edge of expanded tube sheet 4 and fin 6. Further, if desired, thetube sheets may be expanded prior to assembly with the fins and theopening 7 may then be so designed as to eliminate the openings 40.

In order to further clarify the invention there follows anotherembodiment thereof describing the manufacture of a radiant heater forhome use in which the heater is designed to be positioned adjacent thebase board about the walls of the room. Such a heater may bemanufactured, for instance, by sandwiching a pattern 3 between sheets 1and 2 and pressure welding to form a tube sheet 4 by hot rolling theassembly all substantially as set forth in the foregoing embodiment. Theedges of the tube sheet 4 are likewise pried open mechanically asillustrated at 5, FIGURE 3, to facilitate the application of fluidpressure.

The tube sheet 4 is then placed in a die having one unrecessed face, andone face recessed in accordance with the pattern of the separationmaterial within the sheet, and fiuid pressure is then applied throughthe openings 5. The resulting tube sheet then has the tubes formed byexpansion only on one side of the sheet as illustrated in FIGURE 6 at12. A similar result may be obtained by making, for example, sheet 1many times thicker than sheet 2 so that expansion upon the applicationof fluid pressure occurs only on one side of the sheet and a die in thisinstance is not necessary. Likewise, if other than ovoid orsubstantially round tube walls are desired, any desired contour thereofcan be formed by providing the recesses in the die face plate with thedesired contour. The web 8 of the expanded tube sheet is then bent atsubstantially right angles as at 11 on one side thereof, and is bent asat on the other side thereof. Fins 15 are then secured to the tube sheetby spot welding or brazing the right angle portions 16 of the fins 15 tothe web 8 intermediate the tubes 12, as illustrated in FIGURE 7. Inorder that the fins can be suitably spot-Welded to the web, it isdesirable that the sheets 1 and 2 and fins 15 be formed of an alloy ofrelatively high electrical res-istance and an alloy of 68.50% to 71.50%copper, 1.00% to1.50% manganese, an amount up to 0.05% of iron, anamount up to 0.07% of lead, with impurities not greater than about0.10%, and with the balance zinc is preferred for the purpose. Thisalloy has the advantage that it not only has the necessary electricalresistivity for spot welding techniques but is well suited for thepressure welding or roll bonding operation utilized in forming the tubesheet. Slots or openings as illustrated at 14 in FIG- URE 7 are thenmade in the Web 8 between the tubes 12 and sides 10 and 11. The side 10of the tube sheet is the top of the radiant heater and the side 11 ofthe tube sheet is the bottom of the radiant heater when in position withthe fins toward the wall of the room. The slots 14 facilitate thepassage of air over the tubes and through the fins. The resulting heateralthough having thin Walled tubing is of sturdy efficient design. V

In another embodiment, illustrated in FIGURES 8 and 9, a radiant heaterhaving tubes 12, web 8, slots 14, and sides 10 and 11 formed similar tothe embodiment of FIGURE 7 is provided with fins utilizing the metal ofthe web. In order that this may be accomplished, a tube pattern ofseparation material 3 is sandwiched between sheets 1 and 2 to form thetubes as in the foregoing embodiment but there is also applied in thesame manner a fin pattern of separation material between the strips 3and spaced therefrom of a design such that after pressure welding andupon-expansion the bulges 17 are formed on the web 8 between the tubes12.. The duct 18 is opened after the pressure welding step at the edgeof the sheet as at 5, FIGURE 3, and serves as the means for applyingfluid pressure to form the bulges 17. The die utilized during theexpansion to confine the expansion to only one surface of the sheet, asin the foregoing embodirnent, must have its face recessed to accommodatethe bulges 17 and duct 18 as well as the tubes 12. After the bulges 17have been formed, the ends 19 thereof are out off to open the bulges andprovide the fins 20. As will be noted, each fin 20 is of a tube-likestructure open at each end so that the air may pass therethrough. Thefin pattern may, of course, be of any suitable design and may be appliedto the sheet of metal in the same manner and at the same time the tubepattern is applied. Inasmuch as the fin and tube patterns do not touchone another, there is no passageway. between the tube cavity and thebulges utilized for fins. By forming the fins in this way a much lightermore economical structure is obtained with improved heat transfer due tothe fact that the tubes, web, and fins are all one piece of metal.Further this method of manufacture readily lends itself to continuousoperation and mass production. In manufacture, the tubes and fin bulgesmay be simultaneously expanded by proper application of the fluidpressure and the ends 19 of the fin bulges subsequently cut off, or ifdesired, the fin bulges may be first expanded, the ends 19 thereof thencut off, for example with any suitable milling machine, and the tubesfinally expanded. Further, the bulges 17 may be opened by splittinglengthwise, or by other deformation, to form fin-like projections on theweb.

In another embodiment for forming heat exchange cores for automobilesand the like, as illustrated in FIG- URES 10, 11, and 12, alternate finand tube patterns are sandwiched between two sheets of metal, theassembly is pressure Welded by hot rolling to a reduction in thicknessthereof of at least 35% as set forth in the foregoing embodiments, thefin and tube patterns are opened at the edge of the sheet as illustratedfor strips 3 as at 5 in FIGURE 3, fluid pressure is applied to expandwithin a die having suitably recessed face plates those areas of thesheet containing the separation material, and the ends 19 of the finbulges are cut off, all substantially as described in the foregoingembodiments. In FIGURE 10 the top row of fin bulges are illustratedprior to the operation of cutting off the ends 19,-whi1e in the lowertwo rows of bulges the ends 19 have been removed to provide the fins 20.Upon removal of the ends 19 from the top row of fin bulges 17 theresulting expanded tube sheet then has alternate rows of tubes 12 andfins 29. In this embodiment both sides of the sheet are permitted to ex:pand so that the tubes 12 andfins 20 appear as bulges on both sides ofthe sheet, as illustrated in FIGURE 11 which shows an end View of aplurality of such sheets assembled face to face as a heat exchange core.Such a core may be utilized in the cooling system of an internalcombustion engine, or the like. Prior to such assembly, the tube sheetsare coated with tin either before or after expansion. The sheets arethen assembled in such fashion that each tube in each sheet contacts arow. of. fins on the adjacent sheets as illustrated in FIGURE llywhichis a top or plan view of the heat exchange core, and FIGURE 12, which isa front or vertical view of the core of FIG- URE 11. i r v The faces ofthe die in which the tube sheets are expanded are provided with recessesso contoured as to provide tubes of hexagonal outline, FIGURE 11, andfins of circular outline, FIGURE 12. The tubes 12 thus present flatsides against which the fins 20 of the adjacent sheet abut. The assemblyis then heated to weld or solder the adjacent sheets together to formthe finished heat exchange core, Both the fins and tubes may have adifferent contour or design it only being necessary that the adjacentsheets can be suitably welded together. The walls of the tubes and thefins are only about half the thickness of the web 8 thus contributing tothe economy of the structure and facilitating heat transfer. With such aconstruction a substantial portion of the total weight of the metal isutilized as radiating surface.

While in the foregoing specific rolling, annealing, and cleaningsequences are described for forming the tube sheets, it will beunderstood that various rolling, anhealing and cleaning techniques,trimming, tacking the sheets together, shaping and other such operationsmay be employed in accordance with this invention between the step ofapplying the separation material and the step of applying the fluidpressure, depending upon the prevailing practice and the physicalcharacteristics desired in the finished product. For instance, the hotand cold rolling may be carried out in a number of steps depending uponthe economics of the situation and available rolling equipment, 'or thecold rolling or annealing, or both, may be omitted entirely. Whereas,the pressure weld is accomplished by hot rolling the assembly inaccordance with the preferred practice set forth herein, it is to beunderstood that some metal sheeting may be suitably pressure weldedmerely by applying sufficient pressure at room temperature and that suchpressure welding technique may be utilized in accordance with thisinvention. Regardless, however, of the intermediate processing used, itis necessary that the metal of the sheets be suitably joined to form onesubstantially uniform layer at all superposed points not held apart bythe separation material prior to application of the fluid pressure.

The process is well suited for continuous operation. For example, thepatterns of the separation material may be applied successively to thesurface of a strip of metal being unwound from a coil, a second strip ofmetal being unwound from another coil may be superposed on thepattern-coated strip, and the strips then tacked together byspot-welding, edge crimping, or the like and fed continuously through aheating furnace and hot rolling mill. After the rolling and other suchprocessing has been completed, the pressure welded strip containing theseparation material is then expanded by applying fluid pressure asdescribed above to the internal metal surfaces coated with separationmaterial and the fins welded thereto or formed by opening theappropriate bulges as described.

.Any suitable separation material may be employed, its chief functionbeing to prevent bonding of the coated surfaces during the weldingoperation. For instance, in addition to the graphite-water glass:mixture set forth in the foregoing, other inorganic ingredients andmixtures may be employed such as zinc oxide, kieselguhr or otherdiatomaceous earths, fiint, talc, powdered quartz, clays, and the likeand mixtures thereof with each other and with graphite and water glassor the'like. The separation material used must, of course, be socompounded as to flow or elongate with the metal and retainuniformlysufficient thickness to prevent bonding where not desired. Likewise,although the embodiment is described in the foregoing with particularreference to certain alloys, the process of this invention is applicableto brass and other copper base alloys and to other metal sheeting, forexample, aluminum, magnesium, steel, and the like adapted to be pressurewelded, As will be apparent from the foregoing, the process of thisinvention permits the fabrication of a sheet of metal provided withinternal ducts or internal passageways of substantially any desireddesign or pattern, which cavitied sheet of metal with appropriateconduit pattern is adapted for use as a lower cost, more efficient heatexchange device than is obtainable with prior processes. Relativelythick low cost sheet stock may be employed since the desired cavity wallthinness may be obtained by thinning of the metal in the immediate areaupon which the fluid pressure is applied. In prior methods, in which thecavity wall was stamped or drawn, the sheet stock used had to besubstantially of the thinness desired in the cavity wall.

The assembly of the tubes and fins can be accomplished mechanically byemploying suitable combs or dies as are available in the art and theresulting heat exchanger has the advantage of having fins both paralleland perpendicular to the tubes therein.

The copper-manganese-iron-lead-zinc alloy set forth hereinbefore isparticularly well suited for such heat exchangers inasmuch as it is wellsuited for the pressure welding operation in forming the tube. sheet andhas suiiicient electrical resistance to permit spot welding of theassembly. It is not necessary to handle individual tubes in accordancewith the present invention and the heat exchanger provided is strong andsturdy even though very thin sheet stock is utilized. The fins may beformed of the web material or secured thereto by spot welding, orutilizing welding agents such as tin, solder, brazing compounds, or thelike, it only being necessary that the fins and sheets be firmlyattached. It is to be understood that the embodiment of the presentinvention as shown and described is only illustrative and that manychanges may be made therein without departing from the spirit and scopeof the invention as set forth in the following claims.

Having thus described the invention what is claimed and desired tosecure by Letters Patent is:

1. In the process of making heat exchangers, the steps which comprisesandwiching a pattern of separation material between two sheets ofmetal, pressure welding the metal of the sheets into a single layer ofmetal in those areas not covered bysaid material by hot rolling theresulting assembly to a reduction in thickness of at least 35%, applyingfluid pressure to the internal surfaces of said resulting sheet heldapart by said material until passageways substantially in accordancewith said pattern form bulges on at least one surface of said sheet,forming slots through the single layer of metal between said bulges andthe edges of said sheet, bending said edges out of the plane of'thesheet to form a support for and define a housing for the portion of thesheet containing said bulges, and welding fins on said single layer ofmetal between said bulges.

2. In the process of making heat exchangers, the steps which comprisesandwiching a tube pattern of separation material and a separate finpattern of separation material between two sheets of metal, pressurewelding the resulting assembly into a single layer of metal in thoseareas not covered by said material, and thereafter applying fluidpressure to the internal surfaces of said resulting sheet held apart bysaid material until passageways substantially in accordance with saidtube pattern have been formed therein and bulges substantially inaccordance with said fin pattern have been formed thereon and providingfins on said sheet by opening said fin bulges to form fin-likeprojections.

3. In the process of making heat exchangers, the steps which comprisesandwiching separation material between two sheets of metal in apredetermined configuration defining a tube pattern, a fin pattern and acommon conduit pattern interconnecting said tube pattern and said finpattern for subsequent simultaneous inflation of all said patterns,pressure welding the resulting assembly into asingle layer of metal inthose areas not covered by said material, applying fluid pressure to theinternal surfaces of said resulting sheet held apart by said materialuntil passageways substantially in accordance with said tube patternhave been formed therein and bulges substantially in accordance withsaid fin pattern have been formed thereon, removing the inflated commonconduit pattern from the inflated sheet, and providing fins on saidsheet by opening said fin bulges to form fin-like projections.

4. In the process of making heat exchangers, the steps which compriseproviding a plurality of tube sheets formed by sandwiching a tubepattern of separation material and a separate fin pattern of separationmaterial between two sheets of metal, pressure welding the two sheetsinto a single layer of metal in those areas not covered by saidmaterial, coating the resulting sheet with a solder and applying fluidpressure to the internal surfaces of said resulting sheet held apart bysaid material until passageways substantially in accordance With saidtube pattern have been formed therein and bulges substantially inaccordance with said fin pattern have been formed there on, andproviding fins on said sheet by opening said fin bulges to form fin-likeprojections; and thereafter assembling said resulting tube sheets faceto face and heating until the assembled tube sheets are solderedtogether.

5. In the process of making heat exchangers, the steps which compriseproviding a plurality of tube sheets formed by sandwiching separationmaterial between two sheets of metal in a predetermined configurationdefining a tube pattern, a fin pattern and a common conduit patterninterconnecting said tube pattern and said fin pattern for subsequentsimultaneous inflation of all said patterns, pressure welding the twosheets into a single layer of metal in those areas not covered by saidmaterial, coating the resulting sheet with a solder and applying fluidpressure to the internal surfaces of said resulting sheet held apart bysaid material until passageways substantially in accordance with saidtube pattern have been formed therein and bulges substantially inaccordance with said fin pattern have been formed thereon, removing theinflated common conduit pattern from the inflated sheet, and providingfins on said sheet by opening said fin bulges to form fin-likeprojections: and thereafter assembling said resulting tube sheets faceto face and heating until the assembled tube sheets are solderedtogether.

6. In the process of making heat exchangers of the type suitable as aradiant heater positioned adjacent the baseboard about the walls of aroom, the steps which comprise sandwiching a pattern of separationmaterial between two sheets of metal, pressure welding the metal of thesheets into a single layer of metal in those areas not covered by saidmaterial by hot rolling the resulting assembly to a reduction inthickness of at least 35%, said pattern being of the configurationdesired for flow of heat exchange fluid in said heater but foreshortenedin the direction of said rolling, applying fluid pressure to theinternal surfaces of said resulting sheet held apart by said materialuntil passageways substantially in accordance with said pattern areformed on only one surface of said sheet, bending opposite edges of saidsheet at an angle away from the flat surface thereof to form a supportfor said sheet and define with the wall surface a housing for saidpassageways, forming slots to permit the passage of air therethroughbetween said passageways and said edges of the sheet, and welding finson said single layer of metal between said passageways.

7. In the process of making heat exchangers, the steps which comprisesandwiching a tube pattern of separation material and a separate finpattern of separation material between two sheets of metal, pressurewelding the resulting assembly into a single layer of metal in thoseareas not covered by said material, and thereafter applying fluidpressure to the internal surfaces of said resulting sheet held apart bysaid material until passageways substantially in accordance with saidtube pattern have been formed therein and bulges substantially inaccordance with said fin pattern have been formed thereon and providingfins on said sheet by cutting off the ends of said bulges.

8. In the process of making heat exchangers, the steps whichcomprise-sandwiching a tube pattern of separation material and aseparate fin pattern of separation material between two sheets of metal,pressure welding the resulting assembly into a single layer of metal inthose areas not covered by said material, and thereafter applying fluidpressure to the internal surfaces of said resulting sheets held apart bysaid material until passageways substantially in accordance with saidtube pattern have been formed therein and bulges substantially inaccordance with said fin pattern have been formed thereon, providingfins on said sheet by opening said fin bulges to form fin-likeprojections and assembling a plurality of such resulting sheets inface-to-face relationship to provide a heat exchanger core.

9. In the process of making heat exchangers, the steps which comprisesandwiching a pattern of separation material between two sheets ofmetal, joining the metal of the sheets into a single layer of metal inthose areas not covered by said material, applying fluid pressure to theinterior surface of said resulting sheet held apart by said materialuntil passageways substantially in accordance with said pattern formbulges on at least one surface of said sheet, forming slots through thesingle layer of metal between the edges of said sheet and the bulgesadjacent said edges, bending said edges out of the plane of the sheet toform a support for and define a housing for the portion of the sheetcontaining said bulges, and providing fins on said single layer of metalbetween said bulges.

10. In the process of making heat exchangers, the steps which comprisesandwiching a pattern of separation material between two sheets ofmetal, joining the metal of the sheets into a single layer of metal inthose areas not covered by said material, said pattern being of theconfiguration desired for flow of heat exchange fluid in saidexchangers, applying fluid pressure to the interior surfaces of saidresulting sheet held apart by said material until passagewayssubstantially in accordance with said pat-tern are formed on only onesurface of said sheet, bending opposite edges of said sheet at an angleaway from the flat surface thereof to form a support for and defining ahousing for the portion of the sheet containing said passageways,forming slots to permit the passage of air therethrough between saidedges of the sheet and said passageways adjacent said edges, andproviding fins on said single layer of metal between said passageways.

11. The process of claim 7 including the step of interposing betweensaid sheets of metal, together with said tube and fin patterns,additional separation material defining a common conduit patterninterconnecting said tube pattern and said fin pattern, and removingsaid common conduit pattern following said application of fiuidpressure. a i 12. The process of claim 8 including the step interposingbetween said sheets of metal, together with said tube and fin patterns,additional separation material defining a common conduit patterninterconnecting said tube pattern and said fin pattern, and removingsaid common conduit pattern following said application of fluidpressure.

References Cited in the file of this patent UNITED STATES PATENTS 29,276Holmes July 24, 1860 Y 1,960,345 Mnrn May 29, 1934 2,024,379 McCraithDec. 17, 1935 2,079,222 Miller May 4, 1937 2,107,435 Birmingham Feb. 8,1938 2,137,044 Dawson Nov. 15, 1938 2,212,481 Sendzimir Aug. 20, 1940Smith Q. Feb. 22, Johnson May 31, Beck July 3, Powell July 21, R-askinJuly 28, Grenell Sept. 28, Sandberg Jan. 31, Simmons Apr. 3, Greer Feb.11,

FOREIGN PATENTS Great Britain Dec, 28, Denmark Apr. 12, Denmark Dec. 3,France June 28,

